1. Field of the Invention
The present invention relates generally to an electrical component having a base body and two outside electrodes, whereby the base body contains a ceramic having a prescribed, specific resistance. The invention is also directed to a method for the manufacture of the electrical component. Over and above this, the invention is directed to the employment of the electrical component.
2. Description of the Related Art
Electrical components of the type described above are known wherein the specific resistance of the ceramic exhibits a negative temperature coefficient and that, consequently, are employed as an NTC (Negative Temperature Coefficient) resistor. Low values of resistance between 50 and 500 Ohms are demanded for the components for specific applications of the NTC resistors, for example in heating technology, industrial electronics or motor vehicle electronics. The resistance of an NTC component is usually recited at 25° Celsius.
Ceramics that comprise a low specific resistance are available for realizing components having the desired, low values of resistance. These ceramics are based on mixed crystals having a spinel structure that are composed of four cations of the group manganese, nickel, cobalt and copper. The cations are mixed with one another in an atomic ratio Mn/Ni/Co/Cu that lies between 65/19/9/7 and 56/16/8/20. The specific resistance of these ceramics lies between 100 and 0.1 Ωcm.
These ceramics have the disadvantage that their resistance is subject to great variation. Further, these ceramics have the disadvantage that their electrical properties, particularly their electrical resistance, are not stable over the long term. The long-term stability of the components is recited as the change in the resistance after storing the components at, for example, a temperature of 70° Celsius over a time span of 10,000 hours. The time-conditioned change in the resistance under these conditions is greater than 2% given the components produced with low-impedance ceramics.
The known components also have the disadvantage that their resistance—due to the simple design (ceramic block or wafer with two outer contact electrodes)—is exclusively dependent on the specific resistance of the ceramic and is therefore subject to corresponding fluctuations in the composition of the ceramic material. The manufacture-conditioned deviation of the actual resistance from the rated resistance can amount to 5% or more.
The German Patent publication DE 2321478 discloses an NTC resistor (thermistor) that comprises a multi-layer structure, whereby electrode layers are separated from one another by ceramic layers. The ceramic layers are thereby printed on the electrode layers with silk-screening as thick-film layers. As a result of the silk-screening process that is employed, the ceramic layers exhibit high variation with respect to their layer thickness, so that the thermistors disclosed by the publication can only be manufactured with exactly prescribed values of resistance with considerable difficulty. The known thermistors thus exhibit wide tolerances with respect to the electrical resistance.
Due to these wide variation in values and the low long-term stability, the known low-impedance NTC resistors are only suited for applications wherein low demands are made of the component tolerances and component stability. For example, the manufacture of making current limiters is one such application.
Further, the combination of a high B-value and low R-value cannot be physically realized.